1. Field of the Invention
The present invention relates to a process for preparing a chilled beverage product, which contains milk and a food acid. The process of the present invention provides a means for making smooth-textured, low viscosity beverage products which contain milk proteins and a food acid, but which exhibit little or no sedimentation.
2. Description of the Prior Art
When formulating a flavored drink containing milk proteins at a low pH of between pH 3.5 and 4.5, which contains milk solids, whey proteins are generally favored because they are soluble under acidic conditions. Acidic, flavored drinks with casein proteins are known to be unstable and produce large amounts of casein precipitate. A process and formulation for flavored low pH milk protein-containing beverages, which provides for significantly improved stability of the casein proteins with 97 to 99% stability is herein disclosed. The explanation of the chemistry is below.
Milk proteins are generally divided into two classes: casein and whey. Casein is generally recognized as being insoluble under acidic conditions around its isoelectric point of about 4.6. This property of milk proteins is well known and is generally exploited in the manufacturing of cheese. Whey protein is more stable in acid solution and tends to offer less of a precipitation problem. A pH of 4.0 or less is desired for the milk beverage, however, to prevent microbial activity and thus allow for a longer shelf life and to provide a basis for fruit flavor.
Where a milk product which contains casein at a pH below 4.6 is desired, additional treatment is required such as the addition of stabilizers or other processes known in the art. Even these known processes have problems of precipitation over time, and require that the product be shaken prior to drinking.
Food grade stabilizers such as pectin, propylene glycol alginate, carboxymethylcellulose, xanthan gum, locust bean and combinations thereof have been used to prevent the sedimentation and coagulation of the milk proteins and to improve stability of the beverages. It is reported that even when these food stabilizers are employed, beverage products containing milk proteins and acid or acidic juice at a pH below 4.5 tend to exhibit undesirable sedimentation/precipitation over time.
It would be desirable to provide a stable acidic, milk based beverage product which shows enhanced stability with little or no sediment or precipitation. This product should be prepared with conventional processing techniques. The present invention discloses a composition and processing technique for an acidic, milk based beverage with enhanced stability.
Known methods for combining acidic fruit juices with milk products have taken several general approaches. Most common is the addition of a stabilizer to the mixture to control precipitation of milk proteins at a lowered pH.
U.S. Pat. No. 2,859,115 to Rivoche describes how mixing fruit juice with milk can cause milk proteins to precipitate, because the fruit juice lowers the pH of the beverage. The reference describes overcoming this problem through he use of stabilizers such as pectin. A food powder is mixed with a colloidal stabilizer such as pectin or algin in water, followed by the addition of an alkaline earth salt such as calcium carbonate. A dry acid powder, such as tartaric acid is then added to initiates gel formation. The stabilized mixture is then mixed with milk and stirred at a controlled shear so that the gel is broken up, and a desired viscosity is reached.
Similar approaches are employed in U.S. Pat. No. 4,031,264 to Arolski, et al., U.S. Pat. No. 4,046,925 to Igoe, and U.S. Pat. No. 4,078,092 to Nishiyama, all employ similar methods of creating a gel-stabilized mixture, which viscosity is then adjusted by the controlled application of mechanical shear. In Arolski, et al., a fruit mash is mixed with milk and the ensuing coagulation is then controlled by the addition of pectin as a stabilizer. The mixture is stirred and sterilized prior to storage. Igoe involves the formulation of a thickening agent from carboxymethyl cellulose, locust bean gum and xanthan gum in admixture. This stabilizer, with sugar, is added to milk, followed by the addition of fruit juice. In Nishiyama sodium carboxymethyl cellulose is added to the fruit juice first to form a juice composition which can then be added to milk to produce a stable milk product.
U.S. Pat. No. 5,648,112 to Yang, et al. describes mixing milk with a food stabilizer under high shear mixing conditions and maintaining a median particle size of less than 0.8 microns to prevent precipitation of milk proteins. Afterward, the pH is reduced to between 3.2 and 4.5 by the addition of food grade acid.
U.S. Pat. No. 3,692,532 to Shenkenburg, et al. describes a process whereby a stabilizer having carboxyl groups is added to milk, followed by the addition of fruit juice. According to the process disclosed, sugar and carboxymethyl cellulose are mixed with milk, and sufficient time allowed for the carboxyl groups of the stabilizer to react with the casein. The described reaction is said to occur at temperatures below 90xc2x0 F., and the resulting mixture is aged, pasteruized and homogenized. The resulting product is stated to be stable at a pH below 5.0.
Another approach to creating a stable milk and fruit juice beverage is employed in U.S. Pat. No. 4,520,036 to Rialland, et al., and U.S. Pat. No. 4,676,988 to Efstathiou, et al. These two refernces describe a process whereby milk is passed through a cation exchange resin. The pH of the milk is thus lowered to a value 3.8 (Rialland, et al.) and to between 3.2 and 1.5 (Efstathiou, et al.).
Lastly, U.S. Pat. No. 4,416,905 to Lundstedt, et al. describes permitting milk to ferment and achieve a pH in the range between 6.2 to 4.9 and then acidifying the beverage to a pH below 4.7, to produce a better tasting butter milk product
It is therefore the object of the present invention to provide a milk protein beverage which contains milk proteins and a food acid, said beverage having a long shelf life and exhibiting little or no sedimentation over time.
It is a further object of the present invention to provide a means for making a milk protein beverage which contains milk proteins and a food acid, said beverage having a long shelf life and exhibiting little or no sedimentation over time.
It is a further object of the present invention to provide a nutritious and flavorful milk protein beverage which exhibits a smooth texture and a low viscosity, and a means for making same.
The present invention relates to a composition and a process for preparing an acidic milk protein based beverage product. The products prepared according to the process of the present invention are stable and do not show sediment or precipitate over time. These products contain from about 0.5% to 5.0% milk proteins and 0.5 to 2.0% of a food stabilizer mixture and a food acid sufficient to lower the pH below 4.5.
The present invention comprises concentrated milk protein which is a dry powder which is reconstituted with water to form a solution of milk proteins, specifically casein and whey. The milk protein may be substituted with other milk products, such as whole milk, skim milk, dehydrated milk powder, etc.
The process of the present invention comprises, as a first step, mixing the milk proteins with a weak base to elevate the pH. The weak base can be a salt of a weak organic acid, such as sodium citrate, sodium malate, sodium lactate or sodium fumerate. Sodium citrate is the preferred weak base additive. The sodium citrate is added to the concentrated milk protein in sufficient amounts to raise the pH to a range of 7.0 to 8.0.
The addition of weak base creates an environment wherein the casein molecules are enhanced in a manner which promotes the association of stabilizer molecules to the surface of the protein. The basic environment also reduces the role of calcium by inhibiting the bridging of calcium with the protein, thus limiting coalescence and sedimentation of the proteins.
Stabilizers are then added to the mixture. Stabilizers employed in the invention include pectin, propylene glycol alginate and others, which consist of acidic hydrocolloids. These acidic hydrocolloids are negative charged bodies when present in the basic environment. The negatively charged hydrocolloids adhere to the surface of casein molecules, forming colloidal complexes which are themselves negatively charged. These colloidal complexes resist agglomeration, and thus remain in stable suspension in the mixture, even at low pH and low viscosity.
The food stabilizer is added under low shear conditions sufficient to form an intimate mixture. These conditions avoid excessive shear for extended periods of time, which can act to break up the negatively charged colloidal complexes, denature the milk proteins and cause foam.
Upon formation of the negatively charged colloidal complexes which effectively stabilize the milk proteins, optional ingredients, such as flavors, colors, sweeteners, vitamin and mineral supplements, microbiological stabilizers, etc. may then be added. The mixture is then homogenized and cooled below 30xc2x0 C., preferably below 10xc2x0 C.
Acid is then added under low shear conditions to the cooled mixture. A food grade acid such as citric acid is added to bring the pH down to between 3.2 and 4.5. The acid is added in a chilled state, generally below 10xc2x0 C. Mixing remains under low-shear conditions, so as not to break up the stable colloidal complexes.
The final product is then packaged and may stored at room temperature or refrigerated.